This application claims the Paris convention priority of Japanese patent application Hei 10-261347 filed on Sep. 16, 1998, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of cutting a plate glass member as a mother material of materials to be pressed for use on a reheat press method, and to a plate glass mother material cutting device, particularly to a method of cutting a plate glass mother material in which a plurality of grooves are scribed/processed beforehand on one main surface, and to a plate glass mother material cutting device.
2. Description of the Related Art
When optical elements such as an optical lens and a prism are formed, press molding is used. Examples of a press molding method mainly include a precision press molding method, a direct press method, and a reheat press method.
The precision press molding method is a molding method of transferring the shape and surface precision of a molding die to a softened glass, and the pressed material. requires no grinding or polishing.
On the other hand, the direct press method, and he reheat press method are molding methods based on the premise that after the press molding the grinding for bringing the shape of the pressed material close to a final product shape, and the polishing for polishing the surface of the pressed material are performed.
Since the precision press molding method is free of the polishing, it is suitable for manufacturing lenses having shapes difficult to polish, such as a non-spherical lens. However, in order to reproduce the shape precision of the molding die, pressing has to be performed when the viscosity during pressing is in a relatively high range of 108 to 1012 dPaxc2x7S, and only the glass material satisfying the condition that it fails to be devitrified at the pressing viscosity can be used. Moreover, problems are that a manufacture device is large-scaled and expensive, and that manufacture cost is raised.
Therefore, in order to manufacture a large amount of glass products while the production cost is suppressed, the direct press method and the reheat press method are suitable.
The direct press method comprises injecting a predetermined amount of molten glass flowing out of a discharge pipe into lower and upper dies of the molding die, and performing pressing at a relatively low viscosity of around 103 dPaxc2x7S. According to this method, the pressed material has a high weight precision, but the method is not suitable for the production of a small amount of a wide variety of products.
On the other hand, the reheat press method comprises preparing a material to be pressed having a predetermined weight, reheating the material to be pressed from a normal temperature, softening the material, and performing press molding by the molding die at the viscosity of around 105 dPaxc2x7S. This method is not suitable for the production of a large amount of a small variety of products, but is suitable for the production of the small amount of the wide variety of products. In the reheat press method, when the weight of the material to be pressed is insufficient as compared with a cavity in the press molding die, the cavity of the molding die is insufficiently filled with the material to be pressed, which causes an elongation defect. Moreover, when the material to be pressed has an excessive weight, another problem occurs that the material overflows the molding die. Therefore, in the reheat press method, the weight adjustment of the material to be pressed is a big problem.
For example, glass materials to be pressed have been heretofore prepared by a method of using a cutting blade to cut the materials out of a plate-like glass mother material (hereinafter referred to as xe2x80x9cthe blade dicing methodxe2x80x9d). The blade dicing method lacks economical property because a part of the glass mother material is necessarily lost as a cutting margin. Moreover, since wear on a blade (cutting blade) is relatively excessive, the blade needs to be frequently replaced. Furthermore, since the blade is deflected during cutting, it is difficult to cut a large number of materials to be pressed having the same size out of one glass mother material, and weight dispersion among the obtained materials to be pressed relatively becomes large.
To solve the above-described problem in the blade dicing method, in recent years, the same applicant as that of the present application has proposed a method, which comprises: processing a plate-like glass mother material in a predetermined manner; applying a local compression to the glass mother material; and cutting the glass mother material by a generated tensile stress to obtain materials to be pressed having predetermined shapes (hereinafter referred to as xe2x80x9cthe local compression cutting methodxe2x80x9d) (see the publication of Japanese Patent Application Laid-Open No. 189424/1998).
When the materials to be pressed are obtained by the local compression cutting method described in the publication, first the plate (flat) glass mother material is prepared in which one main surface is processed to enlarge the local compression (specifically, a groove is formed), and on the other main surface, a notch is formed opposite to the place processed to enlarge the local compression. Subsequently, the glass mother material is laid on a positioning member (corresponding to xe2x80x9cthe auxiliary cutting memberxe2x80x9d in the present specification) so that the main surface with the notch formed therein faces inward (downward). Under this state the local compression is applied to the place processed to enlarge the local compression, and the glass mother material is cut by tensile stresses generated on both sides of the notched portion when the local compression is applied, to obtain the materials to be pressed having desired shapes.
When the materials to be pressed are prepared by the local compression cutting method described in the Japanese Patent Application Laid-Open No. 189424/1998, the above-described problem in the blade dicing method can be eliminated or improved. When the glass mother material is obtained, however, the processing to enlarge the local compression has to be applied. Therefore, the number of manufacture processes to obtain the glass mother material is increased, and additionally a metal die (molding die) for applying the processing is required. As a result, manufacture cost is relatively raised.
Moreover in general, the materials to be pressed for use in the reheat press method are obtained by cutting the plate glass mother material, and as one cutting method, there is a method of using an ultra-hard wheel cutter to scribe the main surface of the plate glass mother material beforehand. FIG. 1 is a side sectional view showing a method of scribing the plate glass mother material. Moreover, FIG. 2 is a view as seen from the front side of the cutter of the scribing method. Furthermore, FIG. 3 is a view showing a concrete shape of a groove formed in the plate glass mother material. In this method, an ultra-hard wheel cutter 51 having a blade tip angle xcex81 advances on a main surface 50a of a plate glass mother material 50 in an arrow direction of FIG. 10, to form a linear groove 52. When the groove 52 is formed, cracks are generated. The cracks include a vertical crack 53 vertical to the main surface 50a, and horizontal cracks 54, 55 substantially parallel with the main surface 50a. Moreover, a surface crack 56 is also generated as shown in FIG. 3.
After the groove 52 is formed, the plate glass mother material 50 is laid on a mounting base so that the main surface 50a with the vertical crack 53 formed therein faces downward, and a predetermined load is applied to a position opposite to the vertical crack 53 on the side of an opposite main surface 50b. Thereby, the vertical crack 53 grows, and tensile stresses F1 of the vertical crack 53 also help to cut the plate glass mother material 50.
Additionally, when the glass type and shape of the plate glass mother material differ, the way how the crack 53, and the like are generated differs. Therefore, even when the same ultra-hard wheel cutter is used to perform scribing with a quantitatively determined pressing force, desirable cracks cannot constantly be formed. Therefore, cut members cannot be obtained with good precision.
Moreover, there is another method of preparing materials to be pressed for use in the reheat press method, which comprises: scribing/processing a plurality of lattice grooves beforehand on one main surface of the plate glass mother material as the mother material of the materials to be pressed; laying the plate glass mother material with the grooves turned downward; pressing portions opposite to the grooves from above by a rod-like indenter; and allowing cracks to grow by stress concentration generated in the grooves to perform cutting.
In this cutting method, during pressing, a phenomenon takes place in which a cut piece rises centering on the groove. When the rising occurs, a problem arises that adjacent cut pieces strike each other and corners are chipped. When the corners are chipped, the materials to be pressed uniform in weight cannot be formed. Additionally, in worse cases, the cut pieces jump to the outside, and another problem is that the operation cannot advance to the next process.
An object of the present invention is to provide a method of manufacturing materials to be pressed in which local compression is utilized so that the materials to be pressed having high weight precision can easily be obtained at lower costs, a method in which the materials to be pressed resulting from the method are used to manufacture glass molded materials, and a local compression cutting device preferable for obtaining the materials to be pressed.
Another object of the present invention is to provide a method of manufacturing a grooved plate glass mother material from which accurate cut members can constantly be formed, a method of manufacturing glass materials, and a method of manufacturing glass optical elements.
Further object of the present invention is to provide a method of cutting a plate glass mother material in which cut pieces can be prevented from rising, and a plate glass mother material cutting device.
To attain the above-described objects, according to the present invention there is provided a method of manufacturing materials to be pressed, which comprises: disposing a plate glass mother material with a groove formed in one main surface on an auxiliary cutting member so that the main surface with the groove formed therein faces inward; subsequently applying a local compression to a site opposite to a site in which the groove is formed from the side of an outer main surface of the glass mother material; and cutting the glass mother material by tensile stresses generated in both sides of the groove when the local compression is applied. In the method, the shape follow-up property of the auxiliary cutting member is selected/determined so that when the groove is formed in only one main surface of the glass mother material, and the local compression is applied to the glass mother material, the glass mother material is cut by the tensile stresses under a state in which the periphery of the groove is in contact with the auxiliary cutting member.
Moreover, to attain the objects, according to the present invention there is provided a method of manufacturing glass molded materials, which comprises: heating/softening/treating the materials to be pressed obtained by the above-described method of manufacturing the materials to be pressed of the present invention; and subsequently performing press molding.
Furthermore, to attain the objects, according to the present invention, there is provided a local compression cutting device for carrying out the above-described method of manufacturing the materials to be pressed of the present invention, which comprises: a fixed board section having a base and an auxiliary cutting member disposed on a top surface of the base on which a material to be cut is laid; and local compression applying means for applying a local compression to the material to be cut laid on the auxiliary cutting member.
Moreover, to attain the objects, according to the present invention, there is provided a method of manufacturing a grooved plate glass mother material, which comprises: a process of pressing a cutter onto one main surface of the plate glass mother material to form a groove including at least a vertical crack, so that the plate glass mother material having the groove can be cut by local stress. In the process, the blade tip angle of the cutter is selected/determined in consideration of the thickness and material of the plate glass mother material so that the vertical crack becomes deeper than a horizontal crack.
In the method of forming the plate glass mother material, in consideration of the thickness and material of the plate glass mother material, the blade tip angle of the cutter is selected/determined so that the vertical crack becomes deeper than the horizontal crack.
Since the vertical crack is formed to become deeper than the horizontal crack, accurate cut members can constantly be formed.
Furthermore, to solve the problems, according to the present invention, there is provided a method of cutting a plate glass mother material in which a plurality of grooves are scribed/processed beforehand on one main surface, which comprises: laying the plate glass mother material with the grooves turned inward; pressing an outer surface of the plate glass mother material with a cushioning member, and pressing portions opposite to the grooves on the outer surface by a pressing indenter having a stretched shape; and cutting the plate glass mother material.
In the cutting method, the plate glass mother material is first disposed with the grooves turned inward. Subsequently, while the outer surface of the plate glass mother material is pressed with the cushioning member, the portions opposite to the grooves on the outer surface are pressurized with the pressing indenter having the stretched shape to cut the plate glass mother material. Thereby, after cutting, cut pieces are prevented from rising.